The present invention relates to a method of installing a plurality of solar cell modules on an installation surface, such as the roof of a house, for photovoltaic power generation, and also relates to a solar cell module for use in a photovoltaic power generation system, particularly solar cell modules installed stepwise on buildings such as a house.
Photovoltaic power generation for converting light energy into electrical energy by using a photoelectric conversion effect has been widely used as means for obtaining clean energy. Besides, with an improvement of the photoelectric conversion efficiency of solar cells, the number of private houses using a photovoltaic power generation system has been increasing.
FIG. 1 is an illustration showing an ordinary structure of a photovoltaic power generation system. In FIG. 1, numeral 101 is a solar cell module designed to provide a predetermined output voltage by connecting a plurality of solar cells in series. A pair of positive and negative output lines of each of these solar cell modules 101 is connected to a pair of positive and negative trunk cables 103. Moreover, connected to this trunk cable 103 is an inverter 104 for converting a DC output of the solar cell modules 101 into an AC output and outputting the AC output. Accordingly, with a structure where a plurality of the solar cell modules 101 are connected in parallel, even if a part of the solar cell modules 101 is broken, it is possible to prevent the entire system from being infeasible.
FIG. 2 is a schematic view showing a conventional example of installation of a plurality of solar cell modules 101. According to prior arts, as shown in FIG. 2, pieces of solar cell modules 101 having an equal output voltage and an equal size, which are necessary for obtaining a required electric energy, are installed so that they are connected in parallel.
The conventional installation method suffers from the following problems. Since the conventional method uses the solar cell modules of a fixed size, an extremely large number of solar cell modules must be installed for constructing a high-power photovoltaic power generation system and thus the number of processes to be performed for wiring increases and the total construction time is extremely long, and the construction cost also increases as an increased number of parts such as terminal boxes is required. Moreover, since only solar cell modules of an equal size can be used, a plurality of solar cell modules can not be installed efficiently according to an installation surface.
By the way, regarding the structures of solar cell modules for use in the photovoltaic power generation systems, although various types of structures have been known, solar cell modules using a metal base such as a stainless steel plate as a rear-side base are suitable for a photovoltaic power generation system for private houses because the metal base can be used as it is for the roof material.
FIG. 3 is a plan view showing the structure of a conventional example of such a solar cell module, and FIG. 4 is a cross section cut along the A—A line of FIG. 3. In these figures, numeral 111 is a metal base made of stainless steel, for example. Two solar cell sub-modules 112 are mounted on the front surface of the metal base 111. Each solar cell sub-module 112 comprises a glass substrate and a plurality of solar cells arranged on the glass substrate, and is mounted on the front surface of the metal base 111 through an EVA resin. In each solar cell sub-module 112, the plurality of solar cells are electrically connected to each other, and one positive wire 113 and one negative wire 113 are drawn from each of the solar cell sub-modules 112.
A raised portion 122 having a first engagement section 121 at its end is formed at one edge of the metal base 111 where the solar cell sub-modules 112 are not mounted (the ridge-side edge when a plurality of solar cell modules are installed stepwise) by bending the metal base 111, and a suspended portion 124 having a second engagement section 123 at its end is formed at the opposing other edge (the eave-side edge when a plurality of solar cell modules are installed stepwise) by bending the metal base 111. Further, in the process of actually installing a plurality of solar cell modules, the first engagement section 121 of the solar cell module positioned on the eave side is brought into engagement with the second engagement section 123 of the solar cell module positioned on the ridge side.
The raised portion 122 includes a base section 125 formed by bending the metal base 111 so that the base section 125 is parallel to the front surface of the metal base 111, and terminal boxes 115 are mounted on both end portions of this base section 125. The positive wire 113 of one of the solar cell sub-modules 112 is connected to a power cable (not shown) in one of the terminal boxes 115, and the negative wire 113 of the other solar cell sub-module 112 is connected to the power cable in the other terminal box 115. The negative wire 113 of the one solar cell sub-module 112 and the positive wire 113 of the of the solar cell sub-module 112 are connected through a member 116 at an upper part of the front surface of the metal base 111. This wiring member 116 is coated with an insulated tape so as to be insulated from the metal base 111, and is further sealed in an EVA resin layer so as not to be exposed to outside air directly. With the connection as mentioned above, the power generated by the solar cells of the respective solar cell sub-modules 112 is outputted.
In the conventional example, the wiring member for connecting the solar cell sub-modules to each other is sealed in the EVA resin layer so that it is shielded from outside air and has weather resistance, but it is hard to obtain long-term reliability by means of only the EVA resin layer.